Surface ablation technique slightly edges out LASIK for treating compound myopic astigmatism

Las Vegas-Results of a study comparing customized PRK plus mitomycin-C (MMC) against customized LASIK indicate that both are excellent techniques for treating compound myopic astigmatism but suggest that the surface ablation procedure may be somewhat superior, said Anelise D. Wallau, MD, here at refractive surgery subspecialty day, part of the annual meeting of the American Academy of Ophthalmology.

Dr. Wallau, a postdoctoral fellow in the Department of Ophthalmology, Federal University of São Paulo, Brazil, reported the results of a prospective, randomized trial she conducted with colleague Marcos Campos, MD. The study had a fellow eye comparison design and enrolled 44 patients undergoing bilateral surgery.

After 6 months, uncorrected visual acuity (UCVA) and best-corrected visual acuity (BCVA) outcomes were similar for both surgical techniques. A tendency for better results was seen with the surface ablation procedure, however, and the PRK-MMC eyes had significantly less induced higher-order aberrations (HOAs), significantly better outcomes in photopic and mesopic contrast sensitivity testing, and better ratings in patient satisfaction questionnaires.

To determine study eligibility, eyes first were screened with corneal topography systems (EyeSys, EyeSys Vision; Orbscan II, Bausch & Lomb) to rule out any ectatic disease. In addition, eyes had to have logMAR best spectacle-corrected visual acuity of 0.0 or better, demonstrate at least 6 months of refractive stability, have an estimated ablation depth of at least 50 µm, and estimated residual corneal pachometry of at least 410 µm.

A microkeratome (M2, Moria) was used for LASIK flap creation, and mechanical de-epithelialization was performed for PRK. The PRK procedure incorporated MMC as a prophylactic measure, with use of 0.002% MMC applied for 60 seconds, followed by copious irrigation with balanced salt solution. All ablations were performed using LASIK technology (CustomCornea, LADARVision system, Alcon Laboratories) with a 6.5-mm optical zone and a 1.25-mm transition zone.

Postoperative treatment included topical antibiotic plus corticosteroid use for 2 weeks, along with artificial tears as necessary. A bandage contact lens was placed on the PRK eyes until re-epithelialization.

No significant differences between the LASIK and PRK-MMC eyes were seen preoperatively with respect to spherical equivalent ([SE], –3.99 versus –3.85 D), total HOAs (0.39 versus 0.38 µm), or ultrasound pachometry (542 versus 544 µm). Ablation depth also was similar for the LASIK and PRK-MMC techniques (73.1 versus 70.7 µm).

After PRK, re-epithelialization was complete in all eyes by day 5. No eyes developed significant haze during follow-up. The worst haze rating in any eye was 1+, which was present in about 15% of PRK eyes at 1 and 3 months but decreased to just 2% at 6 months.

At 6 months, 95% of eyes in both groups had logMar UCVA of 0.0 (20/20) or better, although better levels of uncorrected vision were achieved in a slightly higher proportion of PRK-MMC eyes. A few eyes in each group lost 2 lines of BCVA, whereas more PRK-MMC eyes than LASIK eyes gained BCVA. Mean cycloplegic SE was about 0.5 D in both groups at 6 months.

"However, a plot of the attempted versus achieved SE indicated the results of the PRK-MMC procedure were more precise," Dr. Wallau said.